Infiltration of Slurry and Ammonia Volatilisation

Volatilisation of ammonia (NH3) from slurry applied in the field reduces the fertiliser value of the slurry and is liable to cause a considerable uncertainty in the nitrogen (N) fertiliser efficiency. A better understanding of slurry–soil interactions is needed in order to develop reliable decision support systems for the use of animal slurry as manure. In this field study, infiltration of slurry in the soil was estimated by measuring chloride (Cl−) and ammonium (TAN=NH3+NH4+) concentrations at different depths from 0·5 to 7·5 cm below the soil surface. The NH3 volatilisation was measured using micrometeorological methods and was related to infiltration. Slurry applied to sandy or clay-loam soils infiltrated to 2–2·5 cm. Ammonium and Cl− infiltration could not be related to slurry, soil and climatic variables because the measured infiltration rates were spatially variable. In spite of this spatial variability, the infiltration parameters of TAN explained a large proportion of the variation in NH3 volatilisation. Therefore, reliable models that currently include, wind, soil surface temperature, TAN and pH of applied slurry as parameters for predicting NH3 volatilisation may also benefit by including parameters for TAN infiltration. Models calculations using soil surface TAN concentration, pH and temperature during the volatilisation event are more precise than calculations using air temperature during the study and TAN concentration and pH in slurry at time of application.